1. Field of the Invention
The present invention relates to an acceleration switch.
2. Description of the Related Art
An omnidirectional acceleration switch as disclosed in Japanese Design Registration No. 1310053 (Reference 1 ), which includes a counter electrode inside amass body, has various advantages such as being used as a normally-off and omnidirectional switch and being compact because monocrystalline silicon can be used as a base for production with the use of semiconductor manufacturing technology.
If the acceleration switch is used in, for example, a portable device having only a small capacity battery to save power, the system can be turned off when a human vibration is not detected, that is, when not in use, and the system can be automatically turned on upon detection of vibration, that is, when in use. The wasted use of a battery can therefore be avoided.
In order to detect vibration based on an acceleration and turn ON and OFF the system, it is desired to detect vibration in any direction, and hence an omnidirectional switch is advantageous. Accordingly, as described in Japanese Design Registration No. 1310053, it is desired to support a weight (mass body) by a plurality of beams so that the vibration of the weight may not be one-sided depending on the acceleration.
Such switch is installed in a portable device and the portable device is now downsized more, and hence it is advantageous that the switch has smaller dimensions. Being smaller in dimensions is advantageous also in terms of cost because a manufacturing method therefore typically uses a semiconductor process.
However, in turning ON and OFF the system in response to detection of vibration or acceleration, the magnitude of vibration or acceleration varies depending on applications. For example, in the case of a device such as a pedometer, an acceleration of no more than 2 G is generated in the device, and hence a switch which shows a response to an acceleration of about 1.5 G is required as an acceleration switch for activation. In the case of a mouse for a personal computer, it is necessary to respond to a slight movement of a hand and hence a switch which shows a response to an acceleration of about 0.5 G is required.
An acceleration sensor has met such various requirements on acceleration. Therefore, the acceleration sensor itself has been required to be driven all the time in order to constantly detect an acceleration. However, the acceleration sensor has large current consumption, and there is a drawback that the life is significantly shortened in the case of a battery-driven portable device.